1. Technical Field
The present invention relates to a device of preventing airplanes from colliding with each other and more particularly to a device of suppressing incorrect alarms to be issued from an airplane collision avoidance system installed in a first airplane in order to reduce useless warning operations to be performed by a pilot on the first airplane in relation to the incorrect alarms concerning a second airplane which approaches the first airplane.
2. Description of the Related Art
Hitherto, a large-sized or middle-sized airplane such as an air liner, a commuter or the like is usually equipped with an airplane collision avoidance system for estimating a possibility of causing the airplane (hereinafter referred to as a first airplane) to collide with other airplane which approaches the first airplane (hereinafter referred to as a second airplane) to issue alarms. Such an apparatus is provided with a question device to the second airplane and an ATC transponder adapted to respond to question signals from the second airplane.
On the other hand, a small-sized airplane such as a personal airplane or the like is equipped with an ATC transponder only in view of a problem incurred by installation of apparatus and device.
As is well known from experiences, not only an ATC transponder installed in an airplane flying in the air but also an ATC transponder in an airplane which stays in a waiting state on the airport or an airplane which is ready to start respond to question signals issued from a question device in the airplane collision avoidance system in the surrounding region of the airport where many airplanes are crowded and troubles take place often. In fact, the conventional airplane collision avoidance system from which alarms are frequently issued on the basis of response signals from the ATC transponder installed in an airplane which has no fear of causing a collision in the air has a drawback that it is very troublesome and dangerous for a pilot who requires concentrated attention before/after landing or taking-off. To obviate the foregoing drawback, the inventors invented a system of making a determination as to whether the second airplane stays in a waiting state or not, with reference to a difference between the time of direct receiving of response signals from ATC transponder installed in the second airplane in response to question signals from the airplane collision avoidance system installed in the first airplane and the time of indirect receiving of the same after reflection on the ground and already filed an application for patent with the Patent Office in Japan. However, it has been found that the aforementioned system is incomplete due to unstability in relation to exact receiving of response signals from ATC transponder after reflection on the ground.